This invention relates to an improved system for separating gaseous mixtures by adsorption and desorption in equipment comprising at least two interchangeable adsorbers provided with suitable adsorbents. In such a system, the gaseous mixture is passed under pressure through one end of an adsorber, and a stream of product gases free from the adsorbed impurities is withdrawn from the other end. The flow of the gaseous mixture is switched to another adsorber the moment the concentration of the impurities at a given location in the adsorber exceeds a given value. This invention is particularly directed to the utilization of the residual gas in the charged adsorber subsequent to the switching step.
It is known from German Auslegeschrift 1,769,936 that an adiabatic process can be employed for separating one or more components from gaseous mixtures, using equipment comprising four or five adsorbers, in order to produce (1) a substantially pure stream of gaseous product and (2) a gaseous stream enriched with impurities. In this known process, after an adsorber is charged, a pressure equalization step is conducted with another, previously purged adsorber, so that the pressure in the charged adsorber is lowered, thereby first releasing residual gas in one direction to purge another adsorber. The pressure is then further decreased but with the flow of gas being in the opposite direction to desorb the previously adsorbed components. Then the adsorber is purged, and the pressure is increased therein partly by pressure equalization with a previously charged adsorber, and partly by the introduction of product gas. The adsorber is thus ready again for adsorption.
Inasmuch as known processes require at least four adsorbers and several stages for each adsorber, many valves (at least 31) are also required to direct the sequences of the individual gas streams. Such adsorption facilities are very costly, and because of the complexity of the system and number of valves, are hindered with problems or reliability and maintenance.